So I got confirmation from a reputable source that the FRST Garrett T2 is a specific one of a kind unit both in the inlet and outlet flange, and nothing else will fit there. Replacing it with anything else equivalent in size/performance to keep a "standardish" output and install will require modifying the header outlet and mid section flanges to whatever you put in there. For the header, easiest option is to get an Escort RS Turbo one and add a T3 to T2 adapter, as the ERST flange is a standard T3 one.

I will now try to have an idea of what modern thing can be equivalent in size and performance to the original T2, be it Garret, Holset or whatever, and has the inlets/outlets at the same side, to avoid having to do extra piping to/from filter and intercooler.

Any suggestions/feedback is welcomed.

For the record, standard Garret T2 compressor A/R is 48, Turbine A/R is 47 (Stamped on the casting). I have no data about the wheels.